Olfaction provides critical information to the very young. Olfactory cues guide neonates to feed and permit siblings to be recognized from other conspecifics. Imprinting on maternal or environmental cues occurs early in life when the olfactory system is rapidly developing. Numerous, anatomical, immunocytochemical and molecular genetic studies have advanced out understanding of the changes occurring during early development. Physiological studies, using activity dependent markers, have demonstrated the essential roles of the olfactory bulb and higher olfactory centers in preference learning and imprinting. There is, however, little information about the basic physiological development of the olfactory epithelium or the changes that might occur during preference learning or imprinting. We propose to functionally characterize the developing olfactory epithelium of the zebrafish using conventional electrophysiological and calcium imaging methods and a novel activity-dependent immunolabeling technique. This emerging developmental model was selected because it breeds year- round, fertilization and development occur externally and rapidly and large numbers of time-staged embryos can be maintained. Our first aim is to determine when after fertilization the voltage, calcium and second messenger-gated currents required to transduce an odorant-binding event into an action potential develop. Our second and third aims characterize the temporal development of odor sensitivity and the spatial distribution of odor-stimulated olfactory receptor neurons (ORNs). Odor-stimulated ORNs will be labeled with an ion channel permeant probe, 1-amino-4- guanidobutane (AGB), and anti-AGB IgG antibodies. Complementary electrophysiological and calcium imaging studied will characterize the response properties of developing ORNs in situ and individually. The final aim is to determine the role odor environment play in the functional development of the olfactory epithelium. The studies proposed will help identify the critical periods in the functional development of the olfactory epithelium and may provide insight into the relative roles of environment versus programmed genetic events in normal developmental processes.